The use of diamond as a window material in a laser tool for medical use is known. Diamond is useful as a window material as it has low absorption for infrared wavelengths in order to transmit a high power laser beam. However, diamond is expensive. Diamond windows are discussed in U.S. Pat. No. 9,040,131, which is hereby incorporated by reference.
Various less expensive alternatives have been tried for high transparency windows for lasers at mid-IR wavelengths (3.5-12 micron), particularly CO2 (10.6 micron). These include Ge, GaAs, CdTe, ZnSe, NaCl, and KCl. The window is often coated with AR/AR (internal and external anti-reflective coating).
ZnSe has been found to be the best of these window materials. However the use of these materials in medical applications, including surgery, has been limited as there are questions about biocompatibility.
SiO2 is a biocompatible compound. It has been used in laser windows for wavelengths from around 0.2 to 3.5 microns but has not been suitable for mid-IR wavelengths, due to its low transmissivity at those wavelengths.
A biocompatible coating for windows for mid-IR wavelength lasers has not been found that is easily applied and inexpensive.